Field
This application relates generally to wireless communication and more specifically, but not exclusively, to group scheduling and acknowledgement.
Introduction
Communication networks enable users to exchange messages among several interacting spatially-separated devices. Communication networks may be classified according to geographic scope, which could be, for example, a wide area, a metropolitan area, a local area, or a personal area. Such networks may be designated respectively as a wide area network (WAN), a metropolitan area network (MAN), a local area network (LAN), or a personal area network (PAN). Communication networks also differ according to the switching technique and/or routing technique employed to interconnect the various network apparatuses and devices. For example, a communication network may use circuit switching, packet switching, or some combination of the two. Communication networks can differ according to the type of physical media employed for transmission. For example, a communication network may support wired communication, wireless communication, or both types of communication. Communication networks can also use different sets of communication protocols. Examples of such communication protocols include the Internet protocol (IP) suite, synchronous optical networking (SONET) protocols, and Ethernet protocols.
In general, wireless networks employ intangible physical media in an unguided propagation mode using electromagnetic waves in radio, microwave, infra-red, optical, or other frequency bands. Consequently, wireless networks are better adapted to facilitate user mobility and rapid field deployment as compared to fixed, wired networks. For example, wireless networks readily support network elements that are mobile and have dynamic connectivity needs. The use of wireless networks also may be preferred for scenarios where it is desirable to provide a network architecture having an ad hoc topology, rather than a fixed topology.
A wireless network may be deployed over a defined geographical area to provide various types of services (e.g., voice, data, multimedia services, etc.) to users within that geographical area. In a typical implementation, one or more access points (APs) are deployed to provide wireless connectivity for access terminals (e.g., stations (STAs)) that are operating within the geographical area served by the wireless network.
Some wireless networks implement Multiple Input Multiple Output (MIMO) technology or Multi-User MIMO (MU-MIMO) technology. A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels or streams, where NS≤min {NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
In practice, overhead may be relatively high for uplink (UL) MU-MIMO transmission. For example, in some MU-MIMO systems, for each UL MU-MIMO transmission, an AP needs to send two special clear-to-send (CTS) messages. The first CTS message triggers STAs with buffered data to send requests for a MU-MIMO transmission. The second CTS message indicates the selected access terminals for MU-MIMO transmission based on received requests.
FIG. 1 illustrates an example of this relatively large overhead for an UL MU-MIMO transmission 100. During a first round channel contention, an initiating STA sends a request-to-send (RTS) to indicate that it has UL data to send. The AP then sends an MU-CTS to trigger other STAs with buffered data to send requests for MU-MIMO transmission. During a second round channel contention, the other STAs send RTSs. The AP then sends a global CTS (G-CTS) to indicate the selected STAs for MU-MIMO transmission based on received requests. In this example, STA 1 through STA 3 are selected (e.g., scheduled) to transmit. Finally, the AP sends a global acknowledgement (G-ACK) to acknowledge receipt of the transmission from STA 1 through STA 3.